1. Field of the Invention
This invention relates generally to numerically controlled machine tools having a spindle rotatable about a spindle trunnion axis A. In particular, this invention relates to an apparatus and method for maintaining accuracy of machining operations conducted with a numerically controlled machine tool by taking measurements with the spindle at different angles about the spindle trunnion A axis.
2. Disussion of the Background Art
Once a machine tool has been aligned to desired specifications, it is desirable to monitor that alignment by some means, for changes which would decrease the machine""s accuracy. Once alignment has changed beyond a predetermined amount or tolerance, the machine will be less accurate. Early detection of a change and correction thereof can lessen the event of, and in many cases, entirely prevent, the production of scrap parts.
In the event of a wreck or other mishaps occurring in a machine tool, where it is fairly evident that a change in accuracy is likely to have occurred, it is also very desirable to have an apparatus and method which could quickly determine what alignments change on the machine. With regard to ordinary day-to-day machining operations, accuracy of a machine may not be readily apparent in parts produced, since the parts may still be within tolerance. However, at a subsequent time, a scrap part produced will indicate that realignment of the machine is needed, and this xe2x80x9cpost-processxe2x80x9d fault correction can, in some cases, be a very expensive way to determine the need for machine corrections. In the case of extremely expensive parts, such as aircraft parts, which are often made of exotic alloys and have a very high number of hours involved in machining away stock to produce the finished part, the expense of finding out after a part has been produced that the machine needs alignment, may be very expensive.
It is well-known in the machine tool arts to use a touch trigger probe, which is periodically swapped with the tool in the spindle, to probe and detect where particular surfaces are on a part, for example. One example of the probing of a part to provide information necessary to offset the program within a machine control, to suit the current location of a part, is taught in U.S. Pat. No. 4,796,195, of W. A. Haggerty, issued Jan. 3, 1989. Another example of a machine, which probes a plurality of jig members distributed on a work table of a machine tool, is taught in U.S. Pat. No. 5,220,510, of H. Araki, issued Jun. 15, 1993. In this patent, a reference coordinate system of a machine control is three dimensionally corrected based on jig members which define space lattice points.
With regard to machine alignments, several patents have taught a method for sensing machine alignment through probing a known standard or fixture, then computing where a error in positioning occurs, and printing out specific instructions on the machine control to direct a machine maintenance person as to adjustment to perform. Such an apparatus is shown in U.S. Pat. No. 5,357,450, of R. D. Hemmerle et al., issued Feb. 10, 1994, entitled xe2x80x9cAutomated Maintenance System for Computer Numerically Controlled Machinexe2x80x9d.
Other patents have taught supplying graphical representations for the aid of an operator, such graphical representations being the result of an operational problem sent by particular sensors. An example of controliwith graphical representation of where problems have arisen, is shown in U.S. Pat. No. 5,345,390 of L. E. Grenip, Jr. et al., issued Sep. 6, 1994. Another patent teaching a method and apparatus for diagnosing machines, is shown in U.S. Pat. No. 4,985,857, of A. Bajpai, et al., issued Jan. 15, 1991, and U.S. Pat. No. 4,809,200, of B. V. Moore et al., issued Feb. 28, 1989.
Cincinnati Machine""s artiFACT(trademark) system is a CNC performance monitor system that quickly detects a change in the machine toolls accuracy. The artiFACT(trademark) system include""s an artiFACT(trademark) fixture, NC program, and analysis software for use with a personal computer. The fixture is mounted on a dedicated machine pallet and probe blocks on the fixture are probed with a spindle-mounted trigger type probe, and then the measured data is compared to baseline data in the machine control. Differences outside specified tolerances indicate that certain machine alignments have changed, generating an alert message on the machine control screen. An alert indicates that machine alignments need to be corrected. The personal computer analysis software displays analyses indicating which areas need correcting. The software also plots periodic measured data versus the baseline for a given fixture point for convenient trend analysis.
The Cincinnati Machine artiFACT(trademark) system probes the fixture with the machine spindle probe touching against fixture probe blocks in X, Y, and Z directions. The Cincinnati Machine artiFACT(trademark) system invention overcomes difficulties and, in some cases shortcomings, of the prior art, by providing an easily probed fixture having target blocks for probing in at least three coordinate directions, an NC probe routine program, an NC comparator program, and an analysis program, wherein the analysis program is conveniently run on a personal computer using data gathered from the probe routine and comparator programs. This system provides data indicating squareness of the machine. The Cincinnati Machine artiFACT(trademark) system for 4 axis condition monitoring is described in greater detail in the Operating Parts/Service Manual for Cincinnati Milacron artiFACT(trademark) (ATS) Automatic Test System for Horizontal Machining Centers, Publication No. 123-SP-98092, published originally by Cincinnati Milacron and incorporated herein by reference. It is highly desirable to have a system that indicates condition of the trunnion axis or A axis of the machine about which the spindle rotates.
The present invention provides a fixture, system, and method for automatically and quickly indicating a condition of a trunnion axis A of a computer numerically controlled (CNC) machine and optionally an alert to a machine operator.
The machine tool monitoring fixture has a body preferably constructed of parallel first and second walls and a third wall disposed between, at right angles to, and connected to the first and second walls, the walls all being mounted on a base. First, second, and third probe blocks are mounted on the body at first, second, and third angular positions respectively along an arc circumscribed by a radius about an axis of rotation. The first, second, and third blocks are mounted on an outer surface of one of the first and second parallel walls, the outer surface facing away from an other of the first and second parallel walls. The first, second, and third probe blocks include first, second, and third flat surfaces with respective normals parallel to the axis of rotation and preferably co-planer. The first and second walls have first and second recesses, respectively, in their unattached end and are preferably arcuate with arcuate edges circumscribed about the axis of rotation.
The monitoring system of the present invention is used for monitoring alignment of a spindle trunnion axis of a computer numerically controlled (CNC) machine and includes the fixture and a probe to measure locations of features including the probe blocks on the fixture. The probe is mounted in a tool holder mounted of a spindle of the machine and a CNC controller is used for moving and operating the spindle mounted probe. Means are provided for and measuring, recording, and displaying location data probed by the probe against the flat surfaces. The means is effective to display the location data as a deviation from baseline measurements.
The present invention provides monitoring fixture and a system and method for a quickly and automatically indicating a condition of the trunnion axis or A axis of the machine about which the spindle rotates.